Power transmission

ABSTRACT

A variable displacement rotary van pump has a cam ring which is angularly displaceable relative to the stationary commutating ports of the pump body. Power losses due to trapping of fluid at intermediate adjustments of the cam ring are minimized by a particular cam contour. Both the rise and the fall of the cam in the intake and discharge areas respectively occur in two steps and these steps are unsymmetrical both as to arcuate extent and as to rate of rise and total rise. This permits the commutating ports to be arranged for higher efficiency at all settings of the adjustable cam ring.

United States Patent 1 Pedersen et al.

POWER TRANSMISSION Inventors: Nicholas F. Pedersen, Farmington; Howard V. Fromm, Madison Heights; Melvin L. Kent, Rochester; Don G. Olmstead, Troy, all of Mich.

Sperry Rand Corporation, Troy, Mich.

Filed: NOV. 25, 1970 Appl. No.: 92,741

Assignee:

U.S. Cl. ..4l8/l6, 418/24, 418/150 Int. Cl ..F01c 21/16, F03c 3/00, F040 15/04 Field of Search ..418/ 16, 24-26,

References Cited UNITED STATES PATENTS 11/1966 Kaatz et a1 ..4l'8/150 8/1953 l-lufferd et al. ..418/26 Primary Examiner--Carlton R. Croyle Assistant ExaminerJohn J. Vrablik Attorney--Van Meter and George [5 7 ABSTRACT A variable displacement rotary van pump has a cam ring which is angularly displaceable relative to the stationary commutating ports of the pump body. Power losses due to trapping of fluid at intermediate adjustments of the cam ring are minimized by a particular cam contour. Both the rise and the fall of the cam in the intake and discharge areas respectively occur in two steps and these steps are unsymmetrical both as to arcuate extent and as to rate of rise and total rise. This permits the commutating 'ports to be arranged for higher efficiency at all settings of the adjustable cam ring.

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Melvin Z. Kent?) D011 (1. O/nviwd y/ L i A FTURNFQW POWER TRANSMISSION The rotary sliding vane type of pump is an efiicient, compact, reliable and long-wearing device which finds wide application in hydraulic power systems and for other pumping purposes, similar structures being also used as rotary hydraulic motors. Such devices ordinarily use a cam ring of non-circular contour relative to the rotor axis, and for this reason the throw of the vane is fixed by the contour of the cam ring. It has been proposed to make such devices with a displacement varying capability by arranging to adjust the phase relationship between the cam ring and the commutating ports of the device. This has been impractical heretofore because the use of reasonably efficient commutation porting at full displacement gives rise to serious problems with trapped fluid at intermediate displacement settings. The destructive effects of the fluid trapping can be avoided only by using commutation porting which involves serious power wastage at the full displacement setting.

It is an object of the present invention to provide an improved rotary sliding vane pump or motor in which the displacement may be varied by shifting the angular relationship between the cam ring and the commutation porting and which avoids both the destructive effects of trapped fluid in the operating cycle and also allows the use of reasonably efficient commutation portmg.

This object is achieved by the provision of a rotary vane pump or motor of the type which has a set of commutating ports and a cam ring together with means for varying the angular position of one relative to the other and having that improvement which comprises a cam ring having an inner contour along which the intake surface of the cam rises in two steps and the discharge surface falls in two steps.

IN THE DRAWINGS FIG. 1 is a longitudinal cross section of a pump cartridge incorporating a preferred form of the present invention.

FIG. 2 is a sectional view on line 2-2 of FIG. 1.

FIG. 3 is a diagrammatic view of the basic pump elements showing the parts in a setting of the cam ring for a medium displacement.

FIG.4 is a view corresponding to FIG. 3 showing the parts in a setting for maximum displacement.

FIG. 5 is a view corresponding to FIG. 3 showing the parts in a position for minimum displacement.

FIG. 6 is a cam design chart for a typical cam ring.

FIG. 7 is a pump displacement chart corresponding to the cam design illustrated in FIG. 6.

In the embodiment selected for illustration of the present invention, a rotary pump of the type suitable for pumping fuel in an aircraft is designed as a cartridge capable of installation in a stationary housing carrying inlet and outlet ducts to lead the fuel to and from the pump, such housing forming no part of the present invention. The cartridge comprises a five-part main body comprising a base 10, a first cheek plate 12, a spacer ring 14, a second cheek plate 16, and an end head 18. These parts are clamped together by a series of bolts 20, FIG. 2. Inlet ports 22 are provided in the cheek plates 12 and 16, see FIG. 3, and outlet ports 24 are provided in the base and the end head 18 to communicate via circumferential passages 26 with through outlet ports 28, FIG. 3, in the cheek plates 12 and 16.

Journalled in bushings 30 is a shaft 32 having a drive coupling 34 at its right end, and to which a rotor 36 is splined at 38. The shaft 32 may incorporate suitable passages, generally indicated at 35, for circulating pumped fluid to lubricate and cool the bearings 30. As illustrated in FIG. 2, the rotor 36 carries a plurality, in this case 11, of vanes 39 slidable radially in their respective slots. The arcuate distance between inlet ports 22 and outlet ports 28 constitutes a sealing land substantially equal to the are between adjacent vanes 39 and thus there is an interval during which fluid is trapped in the intervane space. Freely movable circumferentially of the rotor 36 is a cam ring 40 having an internal contour of ovoid configuration, later to be described in detail. Externally, the cam ring 40 has a plurality of recesses 42 spaced in quadrature between lands 44 which may oscillate in contact with the four circular surfaces 46 on the interior of the spacer 14. Intermediate the surfaces 46, there are provided a plurality of abutments 48, each of which carries a radially slidable vane 50 which engages its circular surface 42 of the cam ring 40 and is urged thereagainst by hydraulic pressure transmitted through suitable passages, not illustrated.

FIGS. 3, 4 and 5 illustrate diagrammatically the intermediate, the maximum and the minimum displacement positions of the cam ring relative to the commutating porting. In these figures, the contour of the cam ring is illustrated only in a very general way which can be illustrated more accurately by plots of the cam rise and the pump displacement such as are shown in FIGS. 6 and 7. In order to minimize the trapping of fluid at settings of intermediate or low displacement, the rise and fall of the cam is contoured in a particular fashion. Referring to FIG. 6, it will be seen that the rise along the intake surface of the cam takes place in two steps, a and b, and also the fall along the discharge surface of the cam takes place in two steps, c and d. However, these are not symmetrical as respects intake and discharge. The first step of the intake contour is different from the first step in the discharge contour both as to arcuate extent and as to total throw as well as rate of rise or fall. Likewise, the total rise along the intake contour occurs after a shorter arcuate travel than is required to complete the total fall along the discharge contour.

Contours of which this is typical will result in displacement curves, such as those illustrated in FIG. 7, which illustrate the rates of displacement along the intake and the discharge contours and also the theoretical net displacement of the pump as a whole at various positions of the adjustable cam ring 40. It will be seen that there is a great difference between the shape of the curves for intake and discharge. This results in a considerable decrease in the amounts of fluids trapped between inlet and outlet ports while the shape of a single intervane space is changing, even though the arcuate span of the land between each inlet and outlet port is such as to avoid a direct bypass path at any position of the rotor.

We claim:

1. In a rotary vane pump of the type having a body, a cam ring with intake surfaces and discharge surfaces oscillatahle in the body, an impeller rotatable in the body and carrying radially slidable vanes engaging the cam ring, inlet and outlet ports in the body separated by sealing lands and commutated by the vanes as they pass across the sealing lands, and means for varying the angular position of the cam ring relative to the sealing lands, that improvement which comprises a cam ring having an inner contour along which each intake surface of the cam rises in two steps and each discharge surface falls in two steps.

2. A pump as defined in claim 1 wherein the arcuate length of the first step in the intake surface is different from the arcuate length of the first step in the discharge surface.

3. A pump as defined in claim 1 wherein the total rise of the first step in the intake surface is different from the total fall of the first step in the discharge surface.

4. A pump as defined in claim 1 wherein the rate of rise of the first step in the intake surface is different from the rate of fall of the first step in the discharge surface.

5. A pump as defined in claim I in which the total arcuate length of the intake and discharge surfaces are unequal.

6. A pump as defined in claim 1 wherein the cam ring is shiftable relative to the body and means is provided for applying fluid pressure in a circumferential direction to shift the cam ring. 

1. In a rotary vane pump of the type having a body, a cam ring with intake surfaces and discharge surfaces oscillatable in the body, an impeller rotatable in the body and carrying radially slidable vanes engaging the cam ring, inlet and outlet portS in the body separated by sealing lands and commutated by the vanes as they pass across the sealing lands, and means for varying the angular position of the cam ring relative to the sealing lands, that improvement which comprises a cam ring having an inner contour along which each intake surface of the cam rises in two steps and each discharge surface falls in two steps.
 1. In a rotary vane pump of the type having a body, a cam ring with intake surfaces and discharge surfaces oscillatable in the body, an impeller rotatable in the body and carrying radially slidable vanes engaging the cam ring, inlet and outlet portS in the body separated by sealing lands and commutated by the vanes as they pass across the sealing lands, and means for varying the angular position of the cam ring relative to the sealing lands, that improvement which comprises a cam ring having an inner contour along which each intake surface of the cam rises in two steps and each discharge surface falls in two steps.
 2. A pump as defined in claim 1 wherein the arcuate length of the first step in the intake surface is different from the arcuate length of the first step in the discharge surface.
 3. A pump as defined in claim 1 wherein the total rise of the first step in the intake surface is different from the total fall of the first step in the discharge surface.
 4. A pump as defined in claim 1 wherein the rate of rise of the first step in the intake surface is different from the rate of fall of the first step in the discharge surface.
 5. A pump as defined in claim 1 in which the total arcuate length of the intake and discharge surfaces are unequal. 